﻿<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Canvas雪花散开放大动画特效 - 站长素材</title>

<script type="text/javascript" src="js/jquery.min.js"></script>

<style>
html,body {
    width: 100%;
    height: 100%;
    margin: 0;
    padding: 0;
    overflow: hidden;
}
.container{
    width: 100%;
    height: 100%;
    margin: 0;
    padding: 0;
}</style>
</head>
<body>

<div id="jsi-snow-container" class="container"></div>

<script>
var RENDERER = {
	SNOW_COUNT: {INIT : 100, DELTA : 1},
	BACKGROUND_COLOR : 'hsl(%h, 50%, %l%)', 
	INIT_HUE : 180,
	DELTA_HUE : 0.1,
	
	init : function(){
		this.setParameters();
		this.reconstructMethod();
		this.createSnow(this.SNOW_COUNT.INIT * this.countRate, true);
		this.render();
	},
	setParameters : function(){
		this.$window = $(window);
		
		this.$container = $('#jsi-snow-container');
		this.width = this.$container.width();
		this.height = this.$container.height();
		this.center = {x : this.width / 2, y : this.height / 2};
		this.countRate =  this.width * this.height / 500 / 500;
		this.canvas = $('<canvas />').attr({width : this.width, height : this.height}).appendTo(this.$container).get(0);
		this.context = this.canvas.getContext('2d');
		
		this.radius = Math.sqrt(this.center.x * this.center.x + this.center.y * this.center.y);
		this.hue = this.INIT_HUE;
		this.snows = [];
	},
	reconstructMethod : function(){
		this.render = this.render.bind(this);
	},
	createSnow : function(count, toRandomize){
		for(var i = 0; i < count; i++){
			this.snows.push(new SNOW(this.width, this.height, this.center, toRandomize));
		}
	},
	render : function(){
		requestAnimationFrame(this.render);
		
		var gradient = this.context.createRadialGradient(this.center.x, this.center.y, 0, this.center.x, this.center.y, this.radius),
			backgroundColor = this.BACKGROUND_COLOR.replace('%h', this.hue);
		
		gradient.addColorStop(0, backgroundColor.replace('%l', 30));
		gradient.addColorStop(0.2, backgroundColor.replace('%l', 20));
		gradient.addColorStop(1, backgroundColor.replace('%l', 5));
		
		this.context.fillStyle = gradient;
		this.context.fillRect(0, 0, this.width, this.height);
		
		for(var i = this.snows.length - 1; i >= 0; i--){
			if(!this.snows[i].render(this.context)){
				this.snows.splice(i, 1);
			}
		}
		this.hue += this.DELTA_HUE;
		this.hue %= 360;
		
		this.createSnow(this.SNOW_COUNT.DELTA, false);
	}
};
var SNOW = function(width, height, center, toRandomize){
	this.width = width;
	this.height = height;
	this.center = center;
	this.init(toRandomize);
};
SNOW.prototype = {
	RADIUS : 20,
	OFFSET : 4,
	INIT_POSITION_MARGIN : 20,
	COLOR : 'rgba(255, 255, 255, 0.8)',
	TOP_RADIUS : {MIN : 1, MAX : 3},
	SCALE : {INIT : 0.04, DELTA : 0.01},
	DELTA_ROTATE : {MIN : -Math.PI / 180 / 2, MAX : Math.PI / 180 / 2},
	THRESHOLD_TRANSPARENCY : 0.7,
	VELOCITY : {MIN : -1, MAX : 1},
	LINE_WIDTH : 2,
	BLUR : 10,
	
	init : function(toRandomize){
		this.setParameters(toRandomize);
		this.createSnow();
	},
	setParameters : function(toRandomize){
		if(!this.canvas){
			this.radius = this.RADIUS + this.TOP_RADIUS.MAX * 2 + this.LINE_WIDTH;
			this.length = this.radius * 2;
			this.canvas = $('<canvas />').attr({width : this.length, height : this.length}).get(0);
			this.context = this.canvas.getContext('2d');
		}
		this.topRadius = this.getRandomValue(this.TOP_RADIUS);
		
		var theta = Math.PI * 2 * Math.random();
		
		this.x = this.center.x + this.INIT_POSITION_MARGIN * Math.cos(theta);
		this.y = this.center.y + this.INIT_POSITION_MARGIN * Math.sin(theta);
		this.vx = this.getRandomValue(this.VELOCITY);
		this.vy = this.getRandomValue(this.VELOCITY);
		
		this.deltaRotate = this.getRandomValue(this.DELTA_ROTATE);
		this.scale = this.SCALE.INIT;
		this.deltaScale = 1 + this.SCALE.DELTA * 500 / Math.max(this.width, this.height);
		this.rotate = 0;
		
		if(toRandomize){
			for(var i = 0, count = Math.random() * 1000; i < count; i++){
				this.x += this.vx;
		 		this.y += this.vy;
		 		this.scale *= this.deltaScale;
		 		this.rotate += this.deltaRotate;
			}
		}
	},
	getRandomValue : function(range){
		return range.MIN + (range.MAX - range.MIN) * Math.random();
	},
	createSnow : function(){
		this.context.clearRect(0, 0, this.length, this.length);
		
		this.context.save();
		this.context.beginPath();
		this.context.translate(this.radius, this.radius);
		this.context.strokeStyle = this.COLOR;
		this.context.lineWidth = this.LINE_WIDTH;
		this.context.shadowColor = this.COLOR;
		this.context.shadowBlur = this.BLUR;
		
		var angle60 = Math.PI / 180 * 60,
			sin60 = Math.sin(angle60),
			cos60 = Math.cos(angle60),
			threshold = Math.random() * this.RADIUS / this.OFFSET | 0,
			rate = 0.5 + Math.random() * 0.5,
			offsetY = this.OFFSET * Math.random() * 2,
			offsetCount = this.RADIUS / this.OFFSET;
		
		for(var i = 0; i < 6; i++){
			this.context.save();
			this.context.rotate(angle60 * i);
			
			for(var j = 0; j <= threshold; j++){
				var y = -this.OFFSET * j;
				
				this.context.moveTo(0, y);
				this.context.lineTo(y * sin60, y * cos60);
			}
			for(var j = threshold; j < offsetCount; j++){
				var y = -this.OFFSET * j,
					x = j * (offsetCount - j + 1) * rate;
				
				this.context.moveTo(x, y - offsetY);
				this.context.lineTo(0, y);
				this.context.lineTo(-x, y - offsetY);
			}
			this.context.moveTo(0, 0);
			this.context.lineTo(0, -this.RADIUS);
			this.context.arc(0, -this.RADIUS - this.topRadius, this.topRadius, Math.PI / 2, Math.PI * 2.5, false);
			this.context.restore();
		}
		this.context.stroke();
		this.context.restore();
	},
	render : function(context){
		context.save();
		
		if(this.scale > this.THRESHOLD_TRANSPARENCY){
			context.globalAlpha = Math.max(0, (1 - this.scale) / (1 - this.THRESHOLD_TRANSPARENCY));
			
			if(this.scale > 1 || this.x < -this.radius || this.x > this.width + this.radius || this.y < -this.radius || this.y > this.height + this.radius){
				context.restore();
				return false;
			}
		}
		context.translate(this.x, this.y);
		context.rotate(this.rotate);
		context.scale(this.scale, this.scale);
		context.drawImage(this.canvas, -this.radius, -this.radius);
		context.restore();
		
 		this.x += this.vx;
 		this.y += this.vy;
 		this.scale *= this.deltaScale;
 		this.rotate += this.deltaRotate;
 		return true;
	}
};

$(function(){
	RENDERER.init();
	 $(window).resize(function(){ 
		//this.canvas = 
		debugger;
		//this.canvas.attr({width : this.width, height : this.height})
		RENDERER.width = window.innerWidth;
		RENDERER.height = window.innerHeight;
		//RENDERER.center = {x : window.innerWidth / 2, y : window.innerHeight / 2};

		//RENDERER.canvas.width = window.innerWidth;
		//RENDERER.canvas.height = window.innerHeight;
	 });
});
</script>

<div style="text-align:center;margin:50px 0; font:normal 14px/24px 'MicroSoft YaHei';">
<p>适用浏览器：360、FireFox、Chrome、Opera、傲游、搜狗、世界之窗. 不支持Safari、IE8及以下浏览器。</p>
<p>来源：<a href="http://sc.chinaz.com/" target="_blank">站长素材</a></p>
</div>
</body>
</html>

